The present invention relates to a method of forming an image by an electrochemical deposition.multidot.build-up phenomenon, using a dispersion in which coloring material fine particles are dispersed in an aqueous solvent, and to a device for carrying out the method.
When an image is formed, it is considered that the image thickness may be preferably 2 .mu.m or less, more preferably 1 .mu.m or less in view of the relation between the duplicated area of colors and sharpness of images in order to attain a high image quality (10000DPI level of resolution/color duplication/variable gradation). Accordingly, the average geometry of the image forming material which is a factor providing image structure is needed to be 1 .mu.m or less. If the average geometry of the image forming material is 5 .mu.m or less powders, there occurred a problem on the fluidity. In the view point, it is considered that the powdered image forming material is very difficult in use, and that, on the other hand, the liquid image forming material is useful. As the latter image recording technologies, for example, the silver salt technologies, ink jet technologies, liquid development electrophotography technologies may be exemplified as representative examples.
1) The printing technologies using silver salt is described in H.Tanemura et al., "High image quality color copying system using silver salt photography", Japan Hardcopy '89, proceedings for meeting for reporting researches, p229 etc.
2) The printing technologies using liquid development electrophotography is described in E. B. Caruthers, et al., "Modeling of Liquid Toner Electrical Characteristics", Proceedings of IS&T 10th Int'l. Congress on Advances in Non-Impact Printing Technologies, p204 ('94) etc.
3) The printing technologies using ink jet technique are described-in many papers such as M. Usui, "Development of New System MACH", Japan Hardcopy '96, proceedings for a meeting for reporting researches, p161 etc.
As the conventional technologies which can be seemed to be similar to the present invention comprising forming images utilizing liquid, the following methods have been known.
4) The method of forming images using electrodeposition liquid, in which coloring materials are dispersed in an insulating liquid and an electric double-layer is formed (JP 7-181750 A, JP7-54407 B), the method of forming fine patterns, using an electrodeposition printing technology in which an insulating pattern is arranged on a conductive substrate to be used as a plate, and the electrodeposition offset printing method (JP4-9902 A, JP6-293125, A).
5) Electrolytic development method, which is shown in Electrophotography Society, proceedings for the discussion on researches, p32 (1971) and Electrophotography Society, proceedings for the discussion on researches, p24 (1964.11). The electrolytic development method comprising the steps of reducing zinc oxide by applying 10 V or more of voltage and exposing at the same time, moving the electrons thus produced to a dye precursor dissolved in a color development so as to reduce, and depositing.multidot.coloring the dye on the surface of the zinc oxide film so as to form an image.
Among the conventional printing technologies, the 1) printing technology using silver salt has no problem on image quality and image fastness, but it has problems on the applicability for the uses in offices since the method is the printing process accompanied with chemical reactions and chemically active reagents are used and wastes are produced.
With the 2) ink jet printing technology, the high resolution can not be obtained by the problems on the nozzle diameter and the reliability of printing. Further since the image forming materials are generally aqueous dyes, there are problems on image fastness, safety and normal paper printing characteristics.
With the 3) electrophotography using an insulating liquid development has no problem on image quality, normal paper printing characteristics and image fastness equal to printing. However, since the printing process is complicated, the machine size becomes large and there are problems on safety and reliability. In addition, the safety of the solvent vapor of the hydrocarbon solvents of the development is regarded as a big problems, and there are some cases in which the uses of the technology are strictly restricted by the government.
Since the above conventional electrodeposition printing technologies using an insulating pattern formed on a conductive substrate as a plate, have complicated process such as that a non-image area of an insulating photoresist must be formed by a photolithography process previously, it is difficult to carry out printing by changing image patterns every time, the precision of the device is high, the device is large-scaled, the number of steps are many and many wastes are produced. Therefore, it can not be used only when printing works are carried out when the device is arranged in a well-equipped factory. In addition, the history of the image forming process is easily remained on an substrate, and the reproducibility of fine image record is low. Since the image area is made depression, the fluidity of the particles on the image area is low, and deposition.multidot.build-up selectivity of the particles are lowered, and many liquid component of the image forming materials on the image area will tend to be remained. Accordingly, the viscosity is lowered, and the image forming materials on the image area may fluidize and produce cohesive fail frequently in the transfer process, and a high image quality can not be obtained easily.
The conventional printing technique 5) using the aqueous dye liquid as a electrodeposition liquid has no problem on vapor of organic solvent, and since the minimum picture element is in the order of dye molecule, it is sufficiently small as several 10 .ANG. so that there are no problem on the high resolution. However, since the image area has an aqueous dye as a main component, there remains the problems on image fastness, safety (inhibition of suction by human bodies), high optical density of images.
As mentioned above, the technologies 2) to 5) as well as the technology 1) do not completely meet the requirements required for image forming technologies used in office (i.d., characteristics such as color high image quality of 1000DPI or more/variable gradient, capability of printing on normal paper, image fastness equal to printing, high safety of printed recorded matters and printing machine, few waste products, low running cost, the capability of making small amount and many types of prints easily and low-costly using no unrecyclable plate).